1. Field of the Invention
The present invention relates both to a video disk on which television picture signals are recorded, and to a recording and reproducing apparatus therefor.
2. Background of the Invention
Recently disks for recording information thereon with high density have been developed and have been commercialized. Typical examples thereof are video disks and digital audio disks. The disks are classified into several types. Of those, an optical type of video disk has a spectral distribution such as shown in FIG. 6. Specifically, a television picture signal is recorded by frequency modulation of a carrier wave of 8.1 MHz to make the synchronization chip level 7.6 MHz and make the white level 9.3 MHz. An accompanying audio signal such as a stereo signal, a bilingual signal, or the like, is recorded by frequency modulation of carrier waves at 2.3 MHz and 2.3 MHz. On the other hand, an optical type of digital audio disk has a spectral distribution such as shown in FIG. 7, and an EFM signal of a pulse-code-modulated stereo signal is recorded within a band not higher than about 2 MHz. In the above-mentioned video disk, the band below 2 MHz is substantially empty, and such an EFM signal can be recorded on the video disk with frequency-division multiplexing. In this case, the disk has such spectral distribution as shown in FIG. 8, and it is understood that the respective signals are fully separable.
FIG. 9 is a block diagram of a recording apparatus for the video disk. In the drawing, a television picture signal is processed by a pre-emphasis circuit 1 for pre-emphasizing the high-band component, modulated by a frequency modulator 2, and fed to an adder 3. On the other hand, two-channel audio signals are pre-emphasized by pre-emphasis circuits 4 and 5, modulated by frequency modulators 6 and 7, and fed to the adder 3. Another set of two-channel audio signals are digitized or pulse-code modulated (PCM) by a PCM encoder 8, eight-to-fourteen modulated (EFM) by an EFM encoder 9, filtered by a low-pass filter 10 for removing the unnecessary high-band component, and fed to the adder 3 through a pre-emphasis circuit 11. Accordingly, the adder 3 receives an FM signal of the picture signal, two FM signals of the two-channel audio signals, and an EFM signal of the other two-channel audio signals. These signals are added to each other by the adder 3, passed through a limiter 12 for adjusting the level, and fed to a light modulator 13. As a result, a laser beam emitted from a laser light source 14 is modulated corresponding to the signals and radiated through an objective lens 16 onto an original recording board 17 rotated by a motor 16 so as to record the signals thereon. A technique for producing disks from such an original recording board 17 is commonly known, and detailed description thereof will be omitted.
FIG. 10 is a block diagram of an apparatus for reproducing audio and video signals from such a disk made by the procedure as described above. In the drawing, a laser beam generated from a pickup 23 is radiated through an objective lens 24 onto a disk 22 rotated by a motor 21. The reflected light from the disk 22 is received by the pickup 23 through the objective lens 24 to thereby generate a reproduction signal. The reproduction RF signal is amplified by an amplifier 25. Of the amplified signal, an FM carrier component passed through a band pass filter 26 is fed to a frequency demodulator 27, demodulated thereby, and produced as a picture signal from a de-emphasis circuit 28. FM carrier components passed through band pass filters 29 and 30 are fed to frequency demodulators 31 and 32, demodulated thereby, and produced as two-channel audio signals from de-emphasis circuits 33 and 34, respectively. An EFM signal component separated by a low-pass filter 35 is fed through a de-emphasis circuit 36 successively to an EFM decoder 37 and a PCM decoder 38 to be first EF-demodulated and PC-demodulated thereby, so as to produce two-channel analog audio signals. Accordingly, a TV audience can desirably choose suitable hi-fi audio signals in conjunction with a picture signal.
As the EFM signal, it may be considered to record a digital data signal in place of the audio signal. Unlike the audio signal, the digital data signal is not always continuous, and therefore it is considered advantageous to made the digital signal have a block structure. However, because the clock frequency of the EFM signal is about 44.1 kHz and the frequency of the vertical synchronizing signal is 29.97 Hz, there exists no simple multiply proportional relation between the two. Accordingly, it is difficult to select the position of each data block and the length thereof.